Integrated circuit (IC) cards are well known and they are very often used for identification e.g. to allow an otherwise restricted access to a facility or for allowance of certain financial transactions by the user of such an integrated circuit card.
An integrated circuit card is a card which contains an integrated circuit and which receives and transmits data according to an interface defined e.g. by ISO Standard 7816. Therefore electronic signals, data structure and transmission protocols of the integrated circuit are e.g. defined in ISO 7816-3. ISO 7816 is an international standard which defines characteristic features of such integrated circuit cards. For example ISO 7816-1 defines the physical characteristics of such integrated circuit cards and ISO 7816-3 defines the electronic signals and transmission protocols.
With asynchronous half-duplex character transmission protocol as defined by ISO 7816-3, hereinafter referred to as “T=1 transmission protocol”, if an interface device transmits a command to an integrated circuit card and the integrated circuit card is not able to respond to this command within the defined maximum waiting time, the integrated circuit card has to transmit a WTX-request, hereinafter referred to waiting time extension request, i.e. a S-block requesting a waiting time extension to the interface device.
Usually block frames transmitted by the card may comprise I-blocks as so called information blocks, R-blocks as so called receive ready blocks and S-blocks as so called supervisory blocks. According to the value of certain bit fields within these blocks, they can be coded as different commands or messages.
In particular, the S-block command S(WTX request) is transmitted from the integrated circuit card to the interface device in order to gain an additional working time when a time needed to process the received command exceeds the maximum Character-/Block-Waiting-Time.
The interface device resets a timer for measuring a Character-Waiting-Time or Block-Waiting-Time when the S(WTX request) block is transmitted from the integrated circuit card, so that the waiting time is reset.
In the case of the aforementioned T=1 transmission protocol, the integrated circuit card has to transmit the S(WTX request) block to the interface device before the time taken to process the input command exceeds the maximum waiting time. This means that a central processing unit of a conventional integrated circuit card must stop executing the command being currently executed in order to process a procedure for transmitting the S(WTX request) block. As is well known, the integrated circuit card processes a command according to an application program. For this reason, the procedure for transmitting the S(WTX request) block causes program overhead. In addition, in cases where it is impossible to stop execution of a current input command, the interface card does not receive a response from the integrated circuit card within the work waiting time and treats a current communication state as a communication error. Accordingly, normal communication between the interface device and the integrated circuit card is not completed. This leads to disadvantages and errors in communication of a integrated circuit card and an interface device.